Highly selective and sensitive colorimetric determination of Cr ion by 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol functionalized Au nanoparticles.

In this work, a rapid, selective naked eyes colorimetric chemical probe for the detection of Cr was developed based on functionalization of gold nanoparticles. For this purpose, surface of Au NPs was functionalized using 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol (AMTT). Through colorimetric studies, it was found that in the presence of Cr ions, AMTT-Au NPs instantly aggregated and resulted in a color change of the solution from red to blue. The color change of AMTT-Au NPs due to the aggregation induced by Cr can be seen with even naked eyes and also by UV-Vis spectroscopy with a detection limit of 1.8μM and 0.1μM, respectively. AMTT-Au NPs showed excellent selectivity toward Cr compared to other cations tested, including K, Na, Cs, Fe, Ni, Cu, Co, Zn, Ba, Ca, Mg, Cd, Pb, Hg ions and especially all trivalent lanthanide ions. The absorbance ratio (A/A) was linear toward Cr concentrations in the range of 0.6-6.1μM (R=0.996). The best response was achieved over a pH range of 3-5. Furthermore, the proposed colorimetric method based on AMTT-Au NPs was successfully used for Cr ion detection in plasma sample and some water samples.